The enhancements were mostly for HTML5 and CSS3 features (video, round corners, responsive web design). Here's the issue, with the way Adobe is now selling you are required to upgrade at every version so CS6 is now the last chance to upgrade from CS5. While this policy could change before CS6.5, it is unlikely. The only other option is the Creative Cloud subscription model. Hard to say whether it's worth the upgrade, depends on how serious you are in moving in this type of direction.

If you are learning, I would say no. You are better off not relying on code hinting that DW provides as it can make you lazy. If you know what you are doing, then upgrading makes coding faster so I think it is worth it (I am on the CC license)